As the number of electrically-powered vehicles increases so does the need for “plug in” charging stations. Such vehicles include land-based vehicles (e.g., automobiles, recreational vehicles, etc.) and watercraft. In the case of recreational vehicles and watercraft, users typically need to “plug in” to re-charge their batteries and tend to stay “plugged in” since they also stay in/on the vehicle/watercraft and use the power to operate on-board conventional systems (e.g., lights, appliances, heating and/or air conditioning systems, etc.). Regardless of the user or their vehicle type, the supplier of power to such charging and/or power supply stations wants to charge the user for the power consumed. This means that charging/power stations typically include some type of metering device for measuring the amount of power consumed.
A potential danger associated with charging/power stations arises from leakage currents that can develop from systems on the vehicle that are plugged into a station. Briefly, leakage currents are derived from normal and abnormal connections of the source and safety earth in the charging and metering systems. Electric motor frequency drives and other variable frequency systems generate high dv/dt transients that, in turn, cause leakage currents due to stray capacitances. Leakage currents often flow back to the source through the associated ground conductor. However they can also flow through alternate unintended ground paths that may pose hazards.
In a boating/marina environment, the dangers associated with even small leakage currents is substantial. More specifically, the leakage currents are drawn into the water via various boat hull fittings or other exposed metal in the water (e.g., anchors, propellers, etc.). The water acts as a current sink (i.e., an alternative conducting path) for the leakage currents as they try to find a path back to their source. The leakage currents subject these current sinks to corrosion and pose as a serious shock threat to a swimmer as a mere 50 milliamps of AC current can be lethal.
Current charging and metering systems utilize various “limit-detection and interrupt” devices/systems (e.g., ground fault interrupts or GFIs, residual current devices or RCDs, fuses, etc.). These devices/systems trigger an exception event and eliminate the power available from the source. Many loads cannot be operated with these types of systems because the loads have high leakage currents and, therefore, will generate nuisance trips of a limit-detection and interrupt device. Additionally, faults causing trips of limit-detection and interrupt devices do not allow the operator to “debug” the system because the operations are suspended immediately upon the exceeding of a set limit. This limit is not adjustable by the user or service provider. Finally, mechanical systems that cause faults to be generated do not report data to the service provider, and do not provide detailed information about the duration, measured levels, or other data that is useful in determining and correcting a faulty load.